This invention relates to a wheel speed sensor unit and a wheel bearing assembly carrying the wheel speed sensor unit.
Wheel speed sensors are mounted on wheel bearings to supply wheel speed signals, for example to an ECU of an ABS.
A typical such wheel speed sensor unit includes an encoder mounted on a rotary member of the vehicle, and a sensor mounted on a stationary member so as to oppose the encoder. Japanese patent publication 8-281018 discloses an arrangement in which a flange-like rotary disk is provided on the rotary member outside a seal for sealing the gap between the fixed member and the rotary member, and a multipolar-magnetized encoder is mounted on the outer end face of the disk. The encoder is exposed to the outside.
Japanese utility model publication 7-36288 discloses an arrangement in which an encoder is provided between two rows of raceways on an inner ring of a wheel bearing assembly, and a sensor is inserted in a hole formed in the outer ring so as to oppose the encoder. The encoder is thus mounted in a sealed space.
In the arrangement shown in Japanese patent publication 8-43411, an encoder is arranged on an outer surface of a rotary member on a side inboard of the bearing, a seal member is mounted on the inboard side of the fixed member, and a sensor is mounted inside the seal member so as to oppose the encoder. The encoder is mounted inside the seal member and outside the bearing.
The first arrangement has a drawback that magnetic powder tends to adhere to the surface of the magnetized encoder during use. This may cause deterioration in the pitch accuracy. The second arrangement has a drawback that the axial dimension for mounting the encoder and sensor is not sufficient. In the third arrangement, since the encorder and the sensor have to be arranged inside of the seal member, the axial dimension of the inboard side end of the stationary member has to be accordingly large.
An object of the invention is to provide a rotating speed sensor unit which includes a seal for preventing entry of foreign matter and which takes up smaller mounting space and thus can be mounted on a wheel bearing assembly without increasing the axial dimension of the stationary member, and to provide a wheel bearing assembly having such a sensor unit.